1. Field of the Invention
The present invention relates to a radio communication device, a communication control device, a radio communication system, a radio communication method, and a communication control method.
2. Description of the Related Art
A mobile phone system having a hierarchical cell structure (HCS) has been used. The hierarchical cell structure involves a high-powered base station (macro cell) with a wide coverage and a low-powered base station (micro cell) with a narrow coverage. The high-powered base station is installed in every certain area, for example, and the low-powered base station is installed in a place where radio waves are difficult to reach (e.g. inside a particular building) within the coverage of the high-powered base station.
Further, the sophistication of the mobile phone system is in progress today. For example, HSPA (High Speed Packet Access) having a higher maximum communication speed than W-CDMA (Wideband Code Division Multiple Access) is already put into practical use, and, moreover, the practical use of LTE (Long Term Evolution) compatible with even higher-speed communication is under discussion.
Under such circumstances, it is necessary to install an indoor small low-powered base station (femtocell; its specifications are standardized and already in practical use abroad) with a narrower coverage than the micro cell in close proximity to a user in need of high-speed communication for the following reasons.
(1) For a higher effective communication speed in each terminal, an environment with a high signal-to-noise ratio, namely, a communication environment in which the distance between a base station and a terminal is short is desirable.
(2) For a wider coverage of a mobile phone carrier and greater user capacity, installing an additional low-cost small low-powered base station exhibits better investment efficiency for a carrier than installing an additional macro cell base station.
(3) By allowing the traffic of high-speed data communication by indoor users to flow out from a femtocell to a broadband network such as DSL, the processing load of a carrier's core network can be reduced.
(4) By awarding the advantage of a carrier gained by use of a femtocell to users, a business model that reduces communication fees charged to users becomes feasible.
Japanese Unexamined Patent Application Publication No. 2005-223447 discloses a system for avoiding the situation where a terminal which enters a service is unable to receive the service due to the shortage of a resource because of the concentration of position registration to a particular base station. In this system, a base station counts the number of terminals for which position registration is made and, based on the count result, transmits annunciation information indicating that excessive position registration is occurring to a terminal in the area. Based on the received annunciation information, the terminal selects a macro cell when the cell state is under excessive position registration.